This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our goal is to develop mass spectrometry combined with H/D exchange to study peptide and protein association reactions. Therefore, we chose gramicidin as the subject of our method development of MS methods to study the association of peptides and proteins in solution. We measured the effects of various solvents on the amount of dimer in solution, the outcome of modeling to give the rate constants for the exchange, and the kinetics of monomer/dimer dynamics as revealed by the H/D exchange experiments. We are also comparing the properties of dimeric gramicidin in organic solvents versus in vesicles.